What this MCCB is and what it does
The Siemens 3VM1440-5MH32-0AA0 is a SENTRON molded case circuit breaker (MCCB) — a 3-pole thermal-magnetic unit with a TM120M overcurrent release. It's rated 400 A continuous at 40 °C ambient, and can handle fault currents up to 6 400 A maximum. At 240 V it interrupts 187 kA; at 415 V and 440 V it's rated 121 kA; at 500 V it drops to 76 kA. That SCCR range covers most industrial distribution panels fed from a medium-voltage transformer. The TM120M release means the thermal element handles overload protection and the magnetic element handles short-circuit — no electronic trip unit, no communication, no ground-fault module. It's a straight electromechanical breaker for main or feeder protection where you don't need adjustable trip curves or remote monitoring.
Thermal derating and panel fit
The 400 A rating holds up to 50 °C. Above that, it derates: 392 A at 55 °C, 384 A at 60 °C, 376 A at 65 °C, and 367 A at 70 °C. If your enclosure runs hot — say near a drive cabinet or in a non-climate-controlled electrical room — factor that curve into your load calculation. The breaker dissipates 77 W max, so panel cooling matters in a sealed box. Dimensions: 248 mm high, 138 mm wide, 110 mm deep. That 138 mm width is wider than a standard 3-pole IEC MCB (typically 54 mm) — plan your DIN-rail or mounting-plate layout accordingly. Front protection is IP40, so it's fine for a closed panel; no washdown rating on the front face.
Lifecycle and sourcing
Insulation voltage is rated 800 V, so it's suitable for 480 V and 600 V class systems with headroom. No undervoltage release, no shunt trip, no communication function — it's a basic main breaker or large feeder breaker where you just need overcurrent protection.